1. Field of the Invention
The present invention relates to a structure of an exhaust pipe system of a vehicle, in more detail, an exhaust pipe structure of a vehicle having exhaust performance improved by improving the structure of an exhaust pipe such that exhaust gas discharged from both sides of an engine smoothly flows without interfering with each other.
2. Description of Related Art
The driving method of vehicles is classified into FF, FR, RR, and 4WD etc., in accordance with the position of the engine and whether the driving shaft is connected to the front wheels or rear wheels.
Although the driving methods each have merits and demerits, in general, the FR (Front engine, Rear wheel drive) and FF (Front engine, Front wheel drive) have been widely used for cars.
The engines of cars are classified into a straight engine and a V-type engine in accordance with the arrangement of cylinders. The V-type engine, including cylinders arranged in a V-shape with respect to the crankshaft, makes it relatively easy to reduce the volume of the engine, such that it is applied when there are several cylinders with large displacement.
When the V-type engine is equipped in a vehicle, the pipe structure of the exhaust system is made different in accordance with the driving method of the vehicle.
The exhaust pipe shown in FIG. 1A has a structure for FF type vehicles and the exhaust pipe shown in FIG. 1B has a structure for FR type vehicles.
As shown in FIG. 1B, since FR type vehicles were equipped with an engine with cylinders arranged in the front-rear direction of the vehicles, exhaust pipes could extend from the manifolds at both sides of the engine and an UCC (Underbody Catalytic Converter) 12a and 12b could be disposed at the middle portion of each of the exhaust pipes. However, it was above all possible to reduce interference between exhaust gases by disposing the conjunction of the manifolds 10a and 10b far from the cylinders of the engine.
Combustion gases that are generated by the cylinders in an engine are generated in accordance with the ignition order of the cylinders. The combustion gas is delivered by a difference in density generated when an exhaust valve is opened/closed. This is called exhaust inertia effect, which is a phenomenon that sucks remaining gas in the cylinder right before the exhaust valve is closed, and depends on the shape and arrangement of the exhaust pipe. Exhaust efficiency of combustion gas is reduced, for example, when combustion gas discharged out of a cylinder interferes with combustion gas discharged out of another cylinder gas and flowing through an exhaust pipe. Although it is preferable to make the manifolds of the cylinder sufficiently long, in order to reduce exhaust interference, the exhaust system should be configured such that the exhaust gases discharged from the manifolds at both side join together at a point sufficiently far from the cylinders.
However, as shown in FIG. 1A, the conjunction A of combustion gases discharged from the manifolds 10a and 10b at both sides is positioned ahead of the underbody catalytic converter 12 in FF type vehicles equipped with an engine having cylinders arrange perpendicular to the vehicles, in consideration of the chassis structure and layout. That is, as shown in the figure, FR type vehicles are configured such that combustion gases join after passing through the underbody catalytic converter that filters toxic substances, whereas FF type vehicles are configured such that exhaust gases already join before entering the UCC. Therefore, the structure of the exhaust system of FF type vehicles is more influenced by exhaust interference than the structure of the exhaust system of FR type vehicles.
Since the exhaust pipe of FF type vehicles is relatively short from the manifolds to the conjunction of exhaust gases due to the reasons described above, torque is reduced when the engine runs at a low revolution speed.
Further, although it is possible to reduce exhaust interference by disposing an underbody catalytic converter at a predetermined rear position and the conjunction behind the underbody catalytic converter, in this configuration, the underbody catalytic converter may malfunction due to temperature drop of exhaust gas.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.